title: Rapid transport of muco-inert nanoparticles in cystic fibrosis sputum treated with N-acetyl cysteine.
abstract: OBJECTIVE
  Sputum poses a critical diffusional barrier that strongly limits the efficacy of drug and gene carriers in the airways of individuals with cystic fibrosis (CF). Previous attempts to enhance particle penetration of CF sputum have focused on either reducing its barrier properties via mucolytics, or decreasing particle adhesion to sputum constituents by coating the particle surface with non-mucoadhesive polymers, including polyethylene glycol (PEG). Neither approach has enabled particles to penetrate expectorated sputum at rates previously observed for non-mucoadhesive nanoparticles in human cervicovaginal mucus. Here, we sought to investigate whether a common mucolytic, N-acetyl cysteine (NAC), in combination with dense PEG coatings on particles, can synergistically enhance particle penetration across fresh undiluted CF sputum.
  
  
  METHODS
  We used high-resolution multiple particle tracking to measure the diffusion of uncoated and PEG-coated nanoparticles in native and NAC-treated CF sputum.
  
  
  RESULTS
  We discovered that 200 nm particles, if densely coated with PEG, were able to penetrate CF sputum pretreated with NAC with average speeds approaching their theoretical speeds in water. Based on the rapid penetration of PEG-coated particles in NAC-treated sputum, we determined that the average spacing between sputum mesh elements was increased from 145 ± 50 nm to 230 ± 50 nm upon NAC treatment. Mathematical models based on particle transport rates suggest as much as 75 and 30% of 200 and 500 nm PEG-coated particles, respectively, may penetrate a physiologically thick NAC-treated CF sputum layer within 20 min. Uncoated particles were trapped in CF sputum pretreated with NAC nearly to the same extent as in native sputum, suggesting that NAC treatment alone offered little improvement to particle penetration.
  
  
  CONCLUSIONS
  NAC facilitated rapid diffusion of PEG-coated, muco-inert nanoparticles in CF sputum. Our results provide a promising strategy to improve drug and gene carrier penetration in CF sputum, offering hope for improved therapies for CF.
authors.affiliation: Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, MD, USA.
authors.forename: Jung Soo
authors.initials: JS
authors.lastname: Suk
authors.forename: Samuel K
authors.initials: SK
authors.lastname: Lai
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Boylan
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Dawson
authors.forename: Michael P
authors.initials: MP
authors.lastname: Boyle
authors.forename: Justin
authors.initials: J
authors.lastname: Hanes
mesh_terms: D000111:Acetylcysteine / Q000494:pharmacology*; D000328:Adult; D001692:Biological Transport / Q000187:drug effects*; D003550:Cystic Fibrosis / Q000188:drug therapy*; D004337:Drug Carriers / Q000737:chemistry* / Q000378:metabolism; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D011092:Polyethylene Glycols / Q000737:chemistry / Q000378:metabolism; D013183:Sputum / Q000187:drug effects / Q000378:metabolism*; D055815:Young Adult
chemical_list: D004337:Drug Carriers; D011092:Polyethylene Glycols; D000111:Acetylcysteine